This invention relates, in general, to thermochemical removal of metal from the surface of a workpiece, commonly called scarfing. More particularly, it relates to the making of instantaneous or "flying starts" for scarfing operations. A "flying start", as that term is used throughout the present specification and claims, means the virtually instantaneous starting of a thermochemical reaction on a workpiece which is moving relative to the scarfing machine at its normal scarfing speed, i.e. a speed of from about 6 to 45 meters per minute. The lower end of said range being used for scarfing cold workpieces and the upper end for scarfing hot workpieces.
It is well known in the art that a scarfing reaction is started by preheating the metal workpiece to its molten or ignition temperature -- normally by preheating flames directed on to a relatively small area -- before applying an obliquely directed stream of high velocity scarfing oxygen at the molten puddle. The scarfing oxygen stream has a two-fold purpose, first to effect a thermochemical reaction with the metal, and second to blow away the reacted metal, thereby exposing fresh metal for the scarfing reaction.
Metal rods have long been used to obtain faster starts in hand scarfing operations, as shown for example by U.S. Pat. No. 2,205,890. Here the work must be stationary, and the operator, by his individual skill, must be able to manipulate both the timing of the scarfing oxygen stream, as well as the angle of the torch and rod. Starting of mechanized scarfing reactions with wire rods is likewise known, as shown by Bucknam et al. in U.S. Pat. No. 2,309,096. Scarfing starts described therein are, however, likewise possible only on stationary workpieces.
Although flying starts are known in the art, making them has only been feasible with complicated, expensive and unreliable processes. As a result, they have met with very little commercial success. Flying starts made with the aid of metal powder are disclosed by DeVries et al. in U.S. Pat. No. 3,216,876, and those made by use of an energized electrode are disclosed by Lobosco in U.S. Pat. No. 2,513,425 and by Svensson et al. in U.S. Pat. No. 3,658,599. Rapid wear of the powder conveying equipment cause powder starts to be unreliable, and this fact plus the cost of the metal powder render powder starts unsatisfactory. The problems associated with electrically powered starts are their expense and relative complexity.
It has not been possible prior to the present invention to make a truly instantaneous or flying start on a moving workpiece without the use of metal powder or an electrically energized metal rod or ceramic electrode.